This invention relates to a dual terminal contact assembly for the starting switch of a dynamoelectric machine (e.g., a fractional horsepower induction motor).
Typically, fractional horsepower induction motors have a stator assembly including a stator core made of a stack of laminations of suitable ferromagnetic material with each of the laminations having a central opening therein and with the central openings forming a longitudinal bore extending through the stator core. A rotor assembly is rotatable within the bore of the stator core and the rotor assembly typically includes a coaxial rotor shaft. The stator assembly further includes end shields or bearing supports for receiving and for journalling the rotor shaft and for holding the rotor centered within the bore of the stator. The stator includes a plurality of coils of wire inserted into slots extending radially outwardly from the bore of the stator core with these coils constituting the windings of the motor. Typically, the windings include different poles or separate windings which may be selectively connected to a source of electrical power for startup of the motor and for operation of the motor at one or more predetermined operational speeds.
Further, such motors are provided with a starting switch actuable by a centrifugal actuator carried by the rotor shaft so as to permit energization of the main windings of the motor and an auxiliary winding during startup of the motor to insure that the motor has sufficient starting torque. Upon the motor attaining a predetermined speed, the centrifugal actuator actuates the starting switch so as to de-energize the auxiliary winding. Upon shutdown or de-energization of the motor, the centrifugal actuator will, upon slowing of the rotor, reset the starting switch so that upon re-energization, the auxiliary winding is again energized. Additionally, the starting switch may include a number of other functions, such as controlling operation of the motor at different speeds of operation. In certain applications, such as electric clothes dryers, other contact sets may be provided in the motor which automatically energize and de-energize the electric heating elements of the clothes dryer upon startup and shutdown of the motor.
Reference may be made to such prior U.S. patents as U.S. Pat. Nos. 3,381,197, 3,691,415, 3,790,730 and 4,284,864 which disclose various fractional horsepower electric motors, centrifugal actuators and starting switches in the same general field as the present invention.
As shown in FIG. 6 of the above-noted U.S. Pat. No. 3,691,415, in some applications, the starting switch is provided with two movable switch arms which make and break circuits with respective fixed contacts. In certain applications, the fixed contacts are electrically connected via lead wires to a common electrical source, such as one of the power leads for the motor. However, the necessity of providing individual lead wires for each of the fixed contacts added considerably to the expense and the complexity of the motor and the requirement of additional lead wires provided additional sources of potential failure due to breakage of the lead wires and the terminals.
In the co-assigned U.S. Pat. No. 4,178,523 to Harold G. Lyerly, a switch jumper strap is disclosed in which a one-piece strip of electrically conductive material was fitted onto the ends of preselected terminals of the starting switch so as to provide a common electrical bus connection between the selected terminals and to eliminate the requirement of external jumper lead wires. While the switch jumper strap disclosed in U.S. Pat. No. 4,178,523 worked well for its intended purpose, it was still necessary that separate terminals for supporting the fixed contacts within the starting switch and a separated switch jumper strap be provided.
Still further, there has been a longstanding need for a terminal in a starting switch which could be readily installed in the starting switch housing, but yet was securely held in place relative to the housing without undue movement of the terminal relative to the housing which could adversely affect operation of the switch.